fix(form-core): set isValidating synchronously before debounce delay

[tt-a1i]

Summary

When async validation is scheduled with debounce, the isValidating flag was being set AFTER an await, causing a gap where callers would see isValidating: false during the debounce period. This caused form.canSubmit to be true when it should be false.

Before (bug):

1. User types value that passes sync validation
2. Async validation is scheduled with 500ms debounce
3. isValidating remains false during the debounce period ← BUG
4. Submit button is enabled when it shouldn't be

After (fix):

1. User types value that passes sync validation
2. Async validation is scheduled with 500ms debounce
3. isValidating is set to true immediately (synchronously)
4. Submit button is correctly disabled

Changes

• Move isValidating = true assignment to happen synchronously, before any await, when async validators are detected
• Add test case to verify isValidating is true during debounce period

Test plan

• Added unit test for the specific scenario (sync passes, async debounced)
• All 363 existing form-core tests pass
• TypeScript compiles without errors

Fixes #1833

AI Assistance Disclosure

I used Codex to review the changes, sanity-check the implementation against existing patterns, and help spot potential edge cases.

[changeset-bot]

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Latest commit: b9dc82f

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---

☁️ Nx Cloud last updated this comment at 2026-01-03 14:13:55 UTC

[pkg-pr-new]

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commit: b9dc82f

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.48%. Comparing base (6892ed0) to head (b9dc82f).
⚠️ Report is 112 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1971      +/-   ##
==========================================
- Coverage   90.35%   89.48%   -0.88%     
==========================================
  Files          38       48      +10     
  Lines        1752     1949     +197     
  Branches      444      488      +44     
==========================================
+ Hits         1583     1744     +161     
- Misses        149      184      +35     
- Partials       20       21       +1     

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[LeCarbonator]

Hmmm ... I think the proposal makes sense. I'll do some digging to see if this is unintentional or not.

Thanks for the PR!